This invention generally relates to electronic switch controls, and more specifically to a method for controlling a plurality of electronic switches employed to connect a motor with an alternating current voltage source.
Single phase, alternating current electric motors have achieved extensive commercial acceptance in many applications, being relatively simple, economical, reliable, and versatile. For example, such motors are often used in refrigeration systems to drive the compressor of the system or to drive one or more of the system fans. Heretofore, individual motors of the general type described above have conventionally been designed to operate at one or, at most, a few discrete speeds. While these motors operate very satisfactorily under a large number of widely differing circumstances, it is nevertheless believed that they may be improved by providing a simple and economical motor control which may be effectively employed to vary the speed of a single phase, alternating current motor over a broad range of values, in a continuous, analog manner. Such a control would enable the motor to operate more efficiently by better matching the motor speed, and thus the power drawn by the motor, to the specific power demand placed thereon.
For this reason, efforts have recently been undertaken to develop a motor control employing a plurality of electronic switch pairs to connect a motor to an alternating current voltage source, and a switch control that actuates these switch pairs in a sequence and manner which develops and rotates a magnetic wave around the motor stator at an adjustable rate, thereby rotating the rotor of the motor at a variable speed. During the development of this motor control, it has been learned that for any given motor speed it is desirable to maximize the number of times that individual switch pairs are actuated as the voltage of the voltage source changes polarity, or passes through a zero voltage value.